Measuring device and method for adjusting the same, and method for obtaining spot size

Abstract

The application provides a measuring device applied to the field of semiconductors, an adjusting method thereof, and a method for acquiring a light spot size. The measuring device comprises a light source, a first adjusting unit, a second adjusting unit, a beam combiner, a light collecting unit, and a detector. The light source is used to generate an excitation light beam and a detection light beam. The first adjusting unit acquires the excitation light beam and adjusts the size of the excitation light beam for expansion. The second adjusting unit acquires the detection light beam and adjusts the size of the detection light beam for expansion. The detector receives a reflection signal of the detection light spot to acquire a detection signal, which is used to feed back a characteristic parameter of the sample to be measured. The diameter of the excitation light beam and the detection light beam is controlled, so that the signal-to-noise ratio of the photoacoustic signal formed by the excitation light and the detection light on the surface of the sample to be measured is improved.

Description

Technical Field

[0001] This invention relates to the field of optical measurement technology, and in particular to a measurement device and its adjustment method, as well as a method for obtaining the spot size, applicable to the semiconductor field. Background Technology

[0002] Acousto-optic measurement systems are used to measure the thickness of metal films, dielectric films, etc. During the measurement process, it is necessary to control the diameters of the excitation and probe beams. When the beam diameter is small, with a fixed beam power, the beam energy density is high. When this energy density reaches optical components, it increases the risk of damage, reduces the lifespan of the components, and increases the safety risks for the testing personnel. Conversely, when the beam diameter is large, the spot size formed on the sample surface is large, the beam energy density is low, and the focused spot size is small. The high energy density of the focused spot allows for better excitation of the photoacoustic effect. Furthermore, the high grayscale value of the spot results in a high signal-to-noise ratio for the spot image, which is beneficial for subsequent adjustment and processing of the spot position.

[0003] Therefore, this invention proposes a measurement device and its adjustment method, as well as a method for obtaining the spot size, applicable to the semiconductor field, to control the diameter of the excitation beam and the probe beam, and / or the final size of the converged spot on the surface of the sample to be measured, thereby improving the signal-to-noise ratio of the photoacoustic signal used for measurement. Summary of the Invention

[0004] This invention provides a measurement device and its adjustment method applied in the semiconductor field, as well as a method for obtaining the spot size, to control the diameter of the excitation beam and the probe beam, and / or the final size of the converged spot on the surface of the sample to be measured, thereby improving the signal-to-noise ratio of the photoacoustic signal used for measurement.

[0005] In a first aspect, the present invention provides a measuring device, comprising: a light source, a first adjustment unit, a second adjustment unit, a beam combiner, a focusing unit, and a detector; the light source is used to generate an excitation beam and a probe beam; the first adjustment unit acquires the excitation beam and expands the excitation beam to an adjustable size; the second adjustment unit acquires the probe beam and expands the probe beam to an adjustable size; the beam combiner receives the excitation beam expanded by the first adjustment unit and the probe beam expanded by the second adjustment unit, and combines the expanded excitation beam and the expanded probe beam; the focusing unit receives the beams combined by the beam combiner to form an excitation spot and a probe spot on the surface of the sample to be measured; the spot sizes of the excitation spot and the probe spot can be adjusted by the first adjustment unit and the second adjustment unit, respectively; the detector receives the reflected signal of the probe spot to obtain a detection signal, the detection signal being used to feed back characteristic parameters of the sample to be measured.

[0006] Its beneficial effects are as follows: by expanding the excitation beam through the first adjustment unit and expanding the probe beam through the second adjustment unit, the excitation beam and the probe beam can be expanded and collimated respectively. The size of the beam can be adjusted according to the required spot size or energy on the sample to be tested, thereby adjusting the size and energy density of the spot formed on the sample to be tested, so as to obtain the required size and energy of the spot, which is beneficial to dynamically improve the range and accuracy of the measurement of thin films.

[0007] Optionally, the excitation beam and the probe beam are obtained from a laser beam emitted by the same laser, or the excitation beam is obtained from a laser beam emitted by a first laser, and the probe beam is obtained from a laser beam emitted by a second laser.

[0008] Optionally, the first adjustment unit includes a chopper and a first beam expander. The chopper receives the excitation beam to modulate its intensity and frequency, and the first beam expander receives the excitation beam after passing through the chopper and expands it. The second adjustment unit includes an optical delay line and a second beam expander. The optical delay line receives the probe beam to adjust its optical path, and the second beam expander expands the probe beam after passing through the optical delay line. Alternatively, the second beam expander expands the probe beam, and the optical delay line receives and transmits the expanded probe beam to adjust its optical path. The advantages are: the excitation beam can be collimated and expanded after passing through the chopper, facilitating the acquisition of a larger beam size, which helps improve the collimation characteristics of the excitation beam and obtain a smaller excitation beam spot; by combining the adjustment of the probe beam with the optical delay line, signal interference caused by beam spot changes can be reduced.

[0009] Optionally, the first beam expanding unit includes M Galilean beam expanders or M Keplerian beam expanders, where M is a positive integer; the second beam expanding unit includes N Galilean beam expanders or N Keplerian beam expanders, where N is a positive integer. Its advantage lies in: determining the spot size of the excitation beam and / or probe beam on the sample surface according to actual measurement needs, and then selecting a suitable design for the required beam magnification.

[0010] Optionally, the measuring device further includes an optical path compensator, which is used to adjust the optical path of the excitation beam. The excitation beam can be transmitted to the first beam expanding unit after passing through the optical path compensator, or the excitation beam can be transmitted to the optical path compensator after passing through the first beam expanding unit. Its advantages are: the optical path compensator can fix the optical path of the excitation beam during multiple film thickness measurements, ensuring the consistency of the excitation pulse on the sample surface (spot size and energy distribution) during measurement, i.e., ensuring the consistency of the excitation signal; it can ensure that the optical paths of the excitation beam and the probe beam are the same; and it can adjust the optical path of the excitation beam on the optical path compensator, achieving flexible control of the optical path and the zero point of the photoacoustic effect.

[0011] Optionally, the distance between the chopper and the laser is less than or equal to the Rayleigh distance of the excitation beam. This has the advantage that the beam expansion of the excitation beam by the first adjustment unit is not limited by the chopper aperture, allowing the excitation beam to be expanded to a larger size, which helps improve the collimation characteristics of the excitation beam and achieve a smaller focused spot size, thereby increasing the energy density of the excitation beam.

[0012] Secondly, the present invention provides a method for obtaining the size of a light spot, applied to a measuring device as described in any of the embodiments of the first aspect above, comprising: calculating a first far-field divergence angle θ1 and a second far-field divergence angle θ2; and obtaining the focal length f of the focusing unit. W According to the focal length f of the focusing unit W The radius r1 of the excitation light spot formed on the sample under test is calculated using the first far-field divergence angle θ1:

[0013] r1=f W tanθ1;

[0014] And according to the focal length f of the focusing unit W The radius r2 of the probe light spot formed on the sample under test is calculated using the second far-field divergence angle θ2:

[0015] r2=f W tanθ2;

[0016] Wherein, the focusing unit is a variable focus focusing unit, the spot size is the size of the excitation light spot and / or the size of the probe light spot; the first far-field divergence angle is the far-field divergence angle of the excitation light beam after the first adjustment unit expands the beam, and the second far-field divergence angle is the far-field divergence angle of the probe light beam after the second adjustment unit expands the beam.

[0017] Its beneficial effect is that, through the method for obtaining the spot size provided by the present invention, the radius of the excitation spot and the probe spot formed on the sample to be tested can be quickly calculated, so as to facilitate the subsequent adjustment of the device.

[0018] Optionally, the method for obtaining the spot size includes: obtaining a first divergence angle and a first angular magnification, and calculating a first far-field divergence angle based on the first divergence angle and the first angular magnification; obtaining a second divergence angle and a second angular magnification, and calculating a second far-field divergence angle based on the second divergence angle and the second angular magnification; wherein, the first divergence angle is the divergence angle of the excitation beam before the first adjustment unit expands the beam, the first angular magnification is the angular magnification of the first adjustment unit, the second divergence angle is the divergence angle of the probe beam before the second adjustment unit expands the beam, and the second angular magnification is the angular magnification of the second adjustment unit.

[0019] Thirdly, the present invention provides a method for obtaining a light spot size, applied to a measuring device as described in any of the embodiments of the first aspect above, comprising: obtaining beam parameters and device parameters in the measuring device, wherein the beam parameters include: the far-field divergence angle of the excitation beam after beam expansion, and the far-field divergence angle of the probe beam after beam expansion; the device parameters are the parameters of the optical devices through which the excitation beam and / or the probe beam propagate and the spatial transmission distance of the excitation beam and / or the probe beam; establishing a light spot size simulation model based on the beam parameters and the device parameters, wherein the light spot size is the excitation light spot size and / or the probe light spot size; and substituting the actual beam parameters and the device parameters obtained through actual measurement into the simulation model to obtain the light spot size of the measuring device.

[0020] Its beneficial effect is that by acquiring a large amount of data to establish a simulation model of the spot size, the actual acquired beam parameters and device parameters can be substituted into the simulation model to improve the accuracy of the spot size solution.

[0021] Optionally, acquiring the beam parameters in the measuring device includes: acquiring a first beam waist spacing and a second beam waist spacing; calculating the diameter of the excitation beam before beam expansion by the first adjustment unit based on the first beam waist spacing; and calculating the diameter of the probe beam before beam expansion by the second adjustment unit based on the second beam waist spacing; calculating the diameter of the excitation beam after beam expansion by the first adjustment unit based on the diameter of the excitation beam before beam expansion and the first magnification, and then calculating the diameter of the excitation beam before the focusing unit; and calculating the diameter of the probe beam after beam expansion by the second adjustment unit based on the diameter of the probe beam before beam expansion and the second magnification, and then calculating the diameter of the probe beam before the focusing unit. Diameter; based on the diameter of the excitation beam before beam expansion and the diameter of the excitation beam after beam expansion, the far-field divergence angle of the excitation beam after beam expansion is obtained; and based on the diameter of the probe beam before beam expansion and the diameter of the probe beam after beam expansion, the far-field divergence angle of the probe beam after beam expansion is obtained; wherein, the first beam waist spacing is the distance between the front focal plane of the first adjustment unit and the beam waist of the excitation beam before beam expansion by the first adjustment unit, the second beam waist spacing is the distance between the front focal plane of the second adjustment unit and the beam waist of the probe beam before beam expansion by the second adjustment unit, the first magnification is the magnification of the first adjustment unit, and the second magnification is the magnification of the second adjustment unit.

[0022] Fourthly, the present invention provides an adjustment method for a measuring device, comprising: acquiring a spot size, wherein the spot size is acquired using the spot size acquisition method described in any of the second aspects above, or using the spot size acquisition method described in any of the third aspects above; setting a threshold range, wherein the threshold range is the range of variation of the spot size; acquiring the calculated spot size formed on the sample to be tested, and determining whether the spot size formed on the sample to be tested is within the threshold range based on the threshold range; if the spot size formed on the sample to be tested is not within the threshold range, adjusting the beam expansion of the excitation beam by the first adjustment unit and / or adjusting the beam expansion of the probe beam by the second adjustment unit, and / or adjusting the focal length of the focusing unit, until the adjusted spot size is within the threshold range, thereby completing the adjustment work.

[0023] Its beneficial effect is that, according to the actual situation, the first adjustment unit can be adjusted to expand the excitation light beam and / or the second adjustment unit can be adjusted to expand the probe light beam, and / or the focal length of the focusing unit can be adjusted to obtain a light spot of the required size. Attached Figure Description

[0024] Figure 1 A schematic diagram of an embodiment of a measuring device provided in this application;

[0025] Figure 2 A schematic diagram of yet another embodiment of the measuring device provided in this application;

[0026] Figure 3 A schematic diagram of another embodiment of the measuring device provided in this application;

[0027] Figure 4 A schematic diagram illustrating yet another embodiment of the measuring device provided in this application;

[0028] Figure 5 A flowchart illustrating an embodiment of a method for obtaining light spot size provided in this application;

[0029] Figure 6 A flowchart illustrating another embodiment of the method for obtaining the spot size provided in this application. Detailed Implementation

[0030] The technical solutions of the embodiments of this application are described below with reference to the accompanying drawings. In the description of the embodiments of this application, the terminology used in the following embodiments is for the purpose of describing specific embodiments only and is not intended to limit the application. As used in the specification and appended claims of this application, the singular expressions "a," "the," "the," "the," and "this" are intended to also include expressions such as "one or more," unless the context clearly indicates otherwise. It should also be understood that in the following embodiments of this application, "at least one" and "one or more" refer to one or more (including two). The term "and / or" is used to describe the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship.

[0031] References to "one embodiment" or "some embodiments" in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized. The term "connection" includes direct connections and indirect connections, unless otherwise stated. "First" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated.

[0032] In the embodiments of this application, the words "exemplarily" or "for example" are used to indicate examples, illustrations, or explanations. Any embodiment or design described as "exemplarily" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design solutions. Specifically, the use of the words "exemplarily" or "for example" is intended to present the relevant concepts in a specific manner.

[0033] In order to obtain a spot size suitable for actual measurement on the surface of a wafer in the semiconductor field, embodiments of this application provide a measurement device and its adjustment method, as well as a method for obtaining the spot size, which are applied in the semiconductor field. The sample to be tested mentioned in this application can refer to a wafer.

[0034] This application provides a measuring device, including: a light source, a first adjustment unit, a second adjustment unit, a beam combiner, a focusing unit, and a detector; the light source generates an excitation beam and a probe beam; the first adjustment unit acquires the excitation beam and expands it to an adjustable size; the second adjustment unit acquires the probe beam and expands it to an adjustable size; the beam combiner receives the excitation beam expanded by the first adjustment unit and the probe beam expanded by the second adjustment unit, and combines the expanded excitation beam and the expanded probe beam; the focusing unit receives the beams combined by the beam combiner to form an excitation spot and a probe spot on the surface of the sample to be measured; the spot sizes of the excitation spot and the probe spot can be adjusted by the first adjustment unit and the second adjustment unit, respectively; the detector receives the reflected signal from the probe spot to obtain a detection signal, which is used to provide feedback on the characteristic parameters of the sample to be measured. Optionally, the focusing unit includes one or more condenser lenses.

[0035] In this embodiment, the excitation beam is expanded by the first adjustment unit and the probe beam is expanded by the second adjustment unit. The excitation beam and the probe beam can be expanded and collimated respectively. The size of the beam can be adjusted according to the required spot size or energy on the sample to be tested, thereby adjusting the size and energy density of the spot formed on the sample to be tested, so as to obtain the required size and energy of the spot, which is beneficial to improving the accuracy of measurement.

[0036] The light source includes a laser. In one possible embodiment, the excitation beam and the probe beam are obtained from a laser beam emitted by the same laser, or the excitation beam is obtained from a laser beam emitted by a first laser, and the probe beam is obtained from a laser beam emitted by a second laser. When the excitation beam and the probe beam are obtained from a laser beam emitted by the same laser, the structure of the measuring device is as follows: Figure 1 As shown, the device includes: a laser 1, a first adjustment unit 2, a second adjustment unit 3, a beam combiner 4, a condenser lens 5, a detector 6, a first reflector 701, a second reflector 702, and a beam splitter 8. The beam splitter 8 is used to split the laser beam emitted by the laser 1 into an excitation beam and a probe beam. The first reflector 701 is used to adjust the propagation direction of the probe beam, and the second reflector 702 is used to adjust the propagation direction of the probe beam after it has been expanded by the second adjustment unit. When the excitation beam and the probe beam are obtained from laser beams emitted by different lasers, the structure of the measuring device is as follows. Figure 2As shown, it includes: a first laser 101, a second laser 102, a first adjustment unit 2, a second adjustment unit 3, a beam combiner 4, a condenser lens 5, a detector 6, and a second reflector 702. The excitation light beam is obtained by the laser beam emitted by the first laser 101, and the detection light beam is obtained by the laser beam emitted by the second laser 102. The function of the second reflector 702 is the same as above.

[0037] In yet another possible embodiment, such as Figure 3 As shown, the measuring device includes, in addition to Figure 1 In addition to the structure shown, the first adjustment unit 2 includes a chopper 201 and a first beam expander 202. The chopper 201 receives the excitation beam to modulate the intensity and frequency of the excitation beam, and the first beam expander 202 receives the excitation beam passing through the chopper and expands the excitation beam. The second adjustment unit 3 includes an optical delay line 301 and a second beam expander 302. The optical delay line 301 receives the probe beam to adjust the optical path of the probe beam, and the second beam expander 302 expands the probe beam passing through the optical delay line; or, the second beam expander 302 expands the probe beam, and the optical delay line 301 receives and transmits the probe beam expanded by the second beam expander 302 to adjust the optical path of the probe beam.

[0038] In this embodiment, the excitation beam can be collimated and expanded after passing through a chopper to obtain a larger beam size, which helps to improve the collimation characteristics of the excitation beam and obtain a smaller excitation beam spot. Furthermore, by adjusting the probe beam in conjunction with the optical delay line, signal interference caused by beam spot changes can be reduced, avoiding the influence of the delay system on the excitation beam path and thus ensuring high stability of the focused beam spot on the sample surface, thereby enhancing the stability of the photoacoustic signal. Figure 3 This is merely to illustrate the general structure of the measuring device and should not be construed as limiting the scope of protection of this application. Furthermore, by first expanding the probe beam and then transmitting it through the optical delay line, the collimation of the probe beam output by the delay system in continuous measurement mode is improved. Simultaneously, a well-designed imaging optical path for the detector to acquire the reflected light spot and a suitable detector are used to ensure that the size of the effective detection surface of the detector is larger than the size of the reflected light spot in front of the detector. This ensures the stability of the signal acquired by the detector, improves the stability of the device, and enhances the signal-to-noise ratio.

[0039] In another possible embodiment, the first beam-expanding unit includes M Galilean beam expanders or M Keplerian beam expanders, where M is a positive integer; the second beam-expanding unit includes N Galilean beam expanders or N Keplerian beam expanders, where N is a positive integer. Appropriate beam-expanding units can be rationally selected and designed according to actual beam-expanding requirements.

[0040] In yet another possible embodiment, the measuring device further includes a reflection unit for controlling the transmission direction of the probe light beam and / or the excitation light beam. Exemplarily, the reflection unit includes a first reflector and a second reflector as described in the corresponding embodiments above.

[0041] In another possible embodiment, the measuring device further includes an optical path compensator for adjusting the optical path of the excitation beam. The excitation beam can be transmitted to the first beam expanding unit after passing through the optical path compensator, or the excitation beam can be transmitted to the optical path compensator after passing through the first beam expanding unit. Figure 4 As shown, the measuring device includes the structures listed above, an optical path compensator 9, and the reflecting unit includes a first reflecting mirror 701, a second reflecting mirror 702, a third reflecting mirror 703, and a fourth reflecting mirror 704. The first reflecting mirror 701 acquires the probe light beam emitted by the light source and adjusts the propagation direction of the probe light beam. The second reflecting mirror 702 acquires and transmits the probe light beam after it has been expanded by the second adjusting unit 3. Furthermore, Figures 1-4 The positional relationship between the detector and the sample is only schematically shown. The positional relationship between the two can be reasonably set and a suitable fixing method can be selected so that the detector can receive the reflected light of the detection light on the sample surface.

[0042] For example, the optical path compensator 9 is used to adjust the optical path of the expanded excitation beam and transmit the expanded excitation beam to the fourth reflector 704. The fourth reflector 704 acquires the expanded excitation beam and transmits it to the beam combiner. In this embodiment, the optical path compensator can fix the optical path of the excitation beam during multiple film thickness measurements to ensure the consistency of the excitation pulse on the sample surface (spot size and energy distribution) during the measurement process, that is, to ensure the consistency of the excitation signal. It is also worth mentioning that the optical path compensator can also ensure that the optical path of the excitation beam and the probe beam from generation to arrival at the sample is equal. Moreover, the optical path compensator 9, the third reflector 703, and the fourth reflector 704 can be flexibly adjusted to control the optical path of the excitation beam and the photoacoustic zero point (the position of the optical delay line when the optical path of the probe beam from generation to arrival at the sample is equal to that of the excitation beam is the photoacoustic zero point). Alternatively, the position of the optical path compensator can be flexibly set so that the excitation light passes through the optical path compensator before being transmitted to the first beam expander unit.

[0043] In practical applications, it is sometimes necessary to adjust the optical path according to actual needs. For example, by changing the optical path length of the probe beam or the excitation beam from its generation to its arrival at the sample, or by adding or removing optical devices, the optical path difference between the probe beam and the excitation beam from its generation to its arrival at the sample may change. In this case, the influence of the optical path length change of the probe beam or the excitation beam on the zero position of the optical delay line can be eliminated by adjusting the optical path compensator.

[0044] In another possible embodiment, the chopper includes at least one of an acousto-optic modulator or an electro-optic modulator. In this embodiment, compared to mechanical modulation choppers, the acousto-optic modulator or the electro-optic modulator exhibits faster response speed (typically on the order of nanoseconds), higher extinction ratio, and better stability in modulating changes in the intensity of the excitation beam. A preferred embodiment is that the chopper is an electro-optic modulator because, compared to the acousto-optic modulator, the electro-optic modulator has a higher extinction ratio (typically greater than 300:1), more stable modulation intensity, better temperature stability, and better spot quality.

[0045] In another possible embodiment, the distance between the chopper and the laser is less than or equal to the Rayleigh distance of the excitation beam. In this embodiment, having the distance between the chopper and the laser less than or equal to the Rayleigh distance of the excitation beam results in a better chopping effect. Furthermore, the Rayleigh distance mentioned in this embodiment can be calculated using the following formula:

[0046] Z R ω is the Rayleigh distance, ω0 is the waist radius of the excitation beam, and λ is the wavelength of the excitation beam before the chopper.

[0047] This application provides a method for obtaining the size of a light spot, applied to the measuring device described in any of the above embodiments, the process of which is as follows: Figure 5 As shown, the specific steps include:

[0048] S501, calculate the first far-field divergence angle θ1 and the second far-field divergence angle θ2.

[0049] S502, Obtain the focal length f of the light-collecting unit. W According to the focal length f of the focusing unit W The radius r1 of the excitation light spot formed on the sample under test is calculated using the first far-field divergence angle θ1:

[0050] r1=f W tanθ1;

[0051] And according to the focal length f of the focusing unit W The radius r2 of the probe light spot formed on the sample under test is calculated using the second far-field divergence angle θ2:

[0052] r2=f W tanθ2.

[0053] Wherein, the focusing unit is a variable focus focusing unit, the spot size is the excitation light spot size and / or the probe light spot size; the first far-field divergence angle θ1 is the far-field divergence angle of the excitation light beam after the first adjustment unit expands the beam, and the second far-field divergence angle θ2 is the far-field divergence angle of the probe light beam after the second adjustment unit expands the beam.

[0054] In this embodiment, the radii of the excitation light spot and the probe light spot formed on the sample to be tested can be quickly calculated, so as to facilitate subsequent adjustments to the device.

[0055] Optionally, the method for obtaining the spot size includes: obtaining a first divergence angle and a first angular magnification, and calculating a first far-field divergence angle based on the first divergence angle and the first angular magnification; obtaining a second divergence angle and a second angular magnification, and calculating a second far-field divergence angle based on the second divergence angle and the second angular magnification; wherein the first divergence angle is the divergence angle of the excitation beam before the first adjustment unit expands the beam, the first angular magnification is the angular magnification of the first adjustment unit, the second divergence angle is the divergence angle of the probe beam before the second adjustment unit expands the beam, and the second angular magnification is the angular magnification of the second adjustment unit. The first angular magnification and the second angular magnification are adjustable parameters.

[0056] For example, assuming the first beam expander is a Keplerian beam expander, then the first beam expander consists of two plano-convex lenses, namely an input plano-convex lens and an output plano-convex lens, wherein the focal length of the input plano-convex lens is f. A1 The focal length of the output plano-convex lens is f. A2 Taking the calculation of the radius of the excitation light spot as an example, the calculation process of the size of the light spot formed on the sample under test is explained as follows:

[0057] θ1=Γ A θ0, where θ1 is the first far-field divergence angle, Γ A θ is the first angular magnification, and θ0 is the first divergence angle, which is the divergence angle of the excitation beam before the first adjustment unit expands the beam. And Γ A =f A1 / f A2 θ0=λ / πω0, where ω0 is the waist radius of the excitation beam and λ is the wavelength of the excitation beam before the chopper.

[0058] Then, the radius of the excitation light spot is calculated as follows:

[0059] r = f W tanθ1, where f W The focal length of the focusing unit is given.

[0060] This embodiment can be achieved by reasonably setting the first far-field divergence angle θ1 and / or adjusting the focal length f of the condenser lens. W This allows for adjustment of the spot size on the wafer surface to adapt to different measurement requirements. Using the same calculation method, the radius of the probe spot can be obtained.

[0061] Although the spot size calculation method provided in the above embodiments can quickly determine the spot size formed on the sample to be tested, its accuracy is insufficient. Therefore, in order to further improve the accuracy of spot size calculation, this application provides another method for obtaining spot size, applied to the measuring device described in any of the above embodiments, the process of which is as follows: Figure 6 As shown, the specific steps include:

[0062] S601, Obtain the beam parameters and device parameters in the measuring device.

[0063] The beam parameters include: the far-field divergence angle of the excitation beam after beam expansion, and the far-field divergence angle of the probe beam after beam expansion; the device parameters are the parameters of the optical devices through which the excitation beam and / or the probe beam propagate, and the spatial transmission distance of the excitation beam and / or the probe beam.

[0064] S602, establish a light spot size simulation model based on the beam parameters and the device parameters, wherein the light spot size is the excitation light spot size and / or the probe light spot size.

[0065] S603, Substitute the actual beam parameters and the device parameters obtained through actual measurement into the simulation model to obtain the spot size of the measuring device. The actual beam parameters are the far-field divergence angle of the expanded excitation beam and the far-field divergence angle of the expanded probe beam, both obtained through actual measurement.

[0066] By establishing a beam size simulation model, more precise beam size can be obtained. By incorporating actual beam parameters (actual output beam quality of the laser) and measured parameters of the device, such as aberrations introduced by optical lenses and other optical components, the intensity and phase distribution of the beam at each position in the optical path can be predicted more accurately. Furthermore, by adjusting adjustable system parameters, such as the inter-lens distance, based on the system optimization objective function, introduced optical aberrations such as spherical aberration can be eliminated, providing possibilities for optical system optimization and reducing or avoiding the impact of measurement device system errors on the measurement signal.

[0067] This method, which establishes a simulation model of the light spot size by acquiring a large amount of experimental data, allows the actual acquired beam parameters and device parameters to be substituted into the simulation model, thereby improving the accuracy of the light spot size calculation.

[0068] In one possible embodiment, acquiring the beam parameters in the measuring device includes: acquiring a first beam waist spacing and a second beam waist spacing; calculating the diameter of the excitation beam before beam expansion by the first adjustment unit based on the first beam waist spacing; and calculating the diameter of the probe beam before beam expansion by the second adjustment unit based on the second beam waist spacing; calculating the diameter of the excitation beam after beam expansion by the first adjustment unit based on the diameter of the excitation beam before beam expansion and the first magnification, and then calculating the diameter of the excitation beam before the focusing unit; calculating the diameter of the probe beam after beam expansion by the second adjustment unit based on the diameter of the probe beam before beam expansion and the second magnification, and then calculating the diameter of the probe beam before the focusing unit; acquiring the far-field divergence angle of the excitation beam after beam expansion based on the diameter of the excitation beam before beam expansion and the diameter of the excitation beam after beam expansion; and acquiring the far-field divergence angle of the probe beam after beam expansion based on the diameter of the probe beam before beam expansion and the diameter of the probe beam after beam expansion. Wherein, the first beam waist spacing is the distance between the front focal plane of the first adjustment unit and the beam waist of the excitation beam before the first adjustment unit expands the beam, the second beam waist spacing is the distance between the front focal plane of the second adjustment unit and the beam waist of the probe beam before the second adjustment unit expands the beam, the first magnification is the magnification of the first adjustment unit, and the second magnification is the magnification of the second adjustment unit.

[0069] For example, the process of obtaining some beam parameters is explained by calculating the propagation path of the excitation beam. The specific calculation process is as follows:

[0070] Calculate the diameter W(Z1) of the excitation beam before the first adjustment unit expands the beam, and ω0[1+(Z1 / ZR1) 2 ] 1 / 2 Where ω0 is the beam waist radius of the excitation beam, Z1 is the first beam waist spacing—that is, the distance between the front focal plane of the first adjustment unit and the beam waist of the excitation beam before the first adjustment unit expands the beam, Z R1 The Rayleigh distance is the distance between the excitation beam and the beam before the first adjustment unit expands the beam when the excitation beam is a Gaussian beam.

[0071] Calculate the diameter W(Z2) of the excitation beam after it has been expanded by the first adjustment unit, where W(Z2) = β A W(Z1), where β A β represents the first amplification rate, i.e., the amplification rate of the first adjustment unit. A =f A2 / f A1Z2 is the distance between the rear focal plane of the first adjustment unit and the waist of the excitation beam before the first adjustment unit expands the beam.

[0072] Calculate the diameter W(Z3) of the excitation beam before the focusing unit, W(Z3) = W(Z2)[1 + (Z3 / Z2)] R2 ) 2 ] 1 / 2 Where Z3 is the distance between the first lens in the focusing unit and the rear focal plane of the first adjustment unit, Z R2 The Rayleigh distance is the distance between the excitation beam and the Gaussian beam after the beam is expanded by the first adjustment unit.

[0073] In another possible embodiment, acquiring the beam parameters and device parameters in the measuring device further includes: acquiring a first far-field divergence angle and a second far-field divergence angle, wherein the first far-field divergence angle is the far-field divergence angle of the excitation beam after beam expansion by the first adjustment unit, and the second far-field divergence angle is the far-field divergence angle of the probe beam after beam expansion by the second adjustment unit.

[0074] In addition, the laser beam quality parameter factor M can be adjusted according to the actual situation. 2 If it is greater than 1, then M can be... 2 Multiply by the wavelength value in all the above formulas.

[0075] According to the beam parametric product BPP, we can obtain: W(Z1)θ0=W(Z2)θ1.

[0076] Calculate the first far-field divergence angle θ1, where θ1 = θ0W(Z1) / W(Z2), and θ0 is the first divergence angle, i.e., the divergence angle of the excitation beam before the first adjustment unit expands the beam. The same calculation method can be used for the probe beam.

[0077] After obtaining the size of the light spot formed on the sample to be tested, if it does not meet the actual requirements, the size of the light spot formed on the sample to be tested can be adjusted using the adjustment method of the measuring device provided in this application embodiment. This is beneficial to dynamically improve the range and accuracy of thin film measurement, and further improve the precision control of semiconductor integrated circuit manufacturing process. The adjustment method specifically includes: obtaining the light spot size, wherein the light spot size is obtained using the light spot size acquisition method described in any of the above claims; setting a threshold range, wherein the threshold range is the range of variation of the light spot size; obtaining the calculated light spot size formed on the sample to be tested, and determining whether the light spot size formed on the sample to be tested is within the threshold range according to the threshold range; if the light spot size formed on the sample to be tested is not within the threshold range, adjusting the beam expansion of the excitation light beam by the first adjustment unit and / or adjusting the beam expansion of the probe light beam by the second adjustment unit, and / or adjusting the focal length of the focusing unit, until the adjusted light spot size is within the threshold range, thus completing the adjustment work.

[0078] The above description is merely a specific implementation of the embodiments of this application, but the protection scope of the embodiments of this application is not limited thereto. Any changes or substitutions within the technical scope disclosed in the embodiments of this application should be covered within the protection scope of the embodiments of this application. Therefore, the protection scope of the embodiments of this application should be determined by the protection scope of the claims.

Claims

1. A measuring device, wherein the measuring device is an acoustic-optical measuring device, characterized in that, include: Light source, first adjustment unit, second adjustment unit, beam combiner, focusing unit, detector; The light source is used to generate an excitation beam and a probe beam; The first adjustment unit acquires the excitation beam and expands the excitation beam in an adjustable manner. The first adjustment unit includes a first beam expanding unit. The second adjustment unit acquires the probe light beam and expands the probe light beam in an adjustable manner. The second adjustment unit includes a second beam expanding unit. The beam combiner receives the excitation beam expanded by the first adjustment unit and the probe beam expanded by the second adjustment unit, so as to combine the expanded excitation beam and the expanded probe beam. The focusing unit receives the beam after it has been combined by the beam combiner to form an excitation light spot and a probe light spot on the surface of the sample to be tested; the size of the excitation light spot and the probe light spot can be adjusted by the first adjustment unit and the second adjustment unit, respectively. The detector receives the reflected signal from the probe light spot to obtain a probe signal, which is used to feed back the characteristic parameters of the sample to be tested; The spot sizes of the excitation light spot and the probe light spot are determined by the following formulas: ， ， in, The radius of the excitation light spot is... The radius of the probe light spot is... The focal length of the light-gathering unit. The first far-field divergence angle is the far-field divergence angle of the excitation beam after it has been expanded by the first adjustment unit. The second far-field divergence angle is the far-field divergence angle of the probe beam after the second adjustment unit expands the beam.

2. The measuring device according to claim 1, characterized in that, The excitation beam and the probe beam are obtained from the same laser beam emitted by the same laser, or the excitation beam is obtained from the laser beam emitted by a first laser and the probe beam is obtained from the laser beam emitted by a second laser.

3. The measuring device according to claim 2, characterized in that, The first adjustment unit includes a chopper and a first beam expander. The chopper receives the excitation beam to modulate the intensity and frequency of the excitation beam, and the first beam expander receives the excitation beam that has passed through the chopper and expands the excitation beam. The second adjustment unit includes an optical delay line and a second beam expander; the optical delay line receives the probe light beam to adjust the optical path of the probe light beam, and the second beam expander expands the probe light beam passing through the optical delay line; or, the second beam expander expands the probe light beam, and the optical delay line receives and transmits the probe light beam expanded by the second beam expander to adjust the optical path of the probe light beam.

4. The measuring device according to claim 3, characterized in that, The first beam expanding unit includes M Galilean beam expanders or M Keplerian beam expanders, where M is a positive integer; The second beam expanding unit includes N Galilean beam expanders or N Kepler beam expanders, where N is a positive integer.

5. The measuring device according to claim 4, characterized in that, It also includes an optical path compensator, which is used to adjust the optical path of the excitation beam. The excitation beam can be transmitted to the first beam expanding unit after passing through the optical path compensator, or the excitation beam can be transmitted to the optical path compensator after passing through the first beam expanding unit.

6. The measuring device according to claim 3, characterized in that, The distance between the chopper and the laser is less than or equal to the Rayleigh distance of the excitation beam.

7. The measuring device according to any one of claims 1 to 6, characterized in that, It also includes a reflection unit for controlling the transmission direction of the probe light beam and / or the excitation light beam.

8. A method for obtaining the size of a light spot, characterized in that, The measuring device used in any one of claims 1 to 7 comprises: Calculate the first far-field divergence angle Second far-field divergence angle ; Obtain the focal length of the focusing unit According to the focal length of the focusing unit and the first far-field divergence angle Calculate the radius of the excitation light spot formed on the sample to be tested. : ； And according to the focal length of the focusing unit and the second far-field divergence angle Calculate the radius of the probe light spot formed on the sample to be tested. : ； Wherein, the focusing unit is a variable focus focusing unit, and the spot size is the excitation light spot size and / or the probe light spot size.

9. The acquisition method according to claim 8, characterized in that, Obtain the first divergence angle and the first angular magnification, and calculate the first far-field divergence angle based on the first divergence angle and the first angular magnification. Obtain the second divergence angle and the second angular magnification, and calculate the second far-field divergence angle based on the second divergence angle and the second angular magnification; Wherein, the first divergence angle is the divergence angle of the excitation beam before the first adjustment unit expands the beam, the first angular magnification is the angular magnification of the first adjustment unit, the second divergence angle is the divergence angle of the probe beam before the second adjustment unit expands the beam, and the second angular magnification is the angular magnification of the second adjustment unit.

10. A method for obtaining the size of a light spot, characterized in that, The measuring device used in any one of claims 1 to 7 comprises: The beam parameters and device parameters in the measuring device are obtained. The beam parameters include the far-field divergence angle of the excitation beam after beam expansion and the far-field divergence angle of the probe beam after beam expansion. The device parameters are the parameters of the optical devices through which the excitation beam and / or the probe beam propagate and the spatial transmission distance of the excitation beam and / or the probe beam. A light spot size simulation model is established based on the beam parameters and the device parameters, wherein the light spot size is the excitation light spot size and / or the probe light spot size; The actual beam parameters and the device parameters obtained through actual measurement are substituted into the simulation model to obtain the spot size of the measuring device.

11. The acquisition method according to claim 10, characterized in that, The process of obtaining the beam parameters in the measuring device includes: Obtain the first beam waist distance and the second beam waist distance, calculate the diameter of the excitation beam before the first adjustment unit expands the beam based on the first beam waist distance, and calculate the diameter of the probe beam before the second adjustment unit expands the beam based on the second beam waist distance; Based on the diameter of the excitation beam before beam expansion and the first magnification, the diameter of the excitation beam after beam expansion by the first adjustment unit is calculated, and then the diameter of the excitation beam before the focusing unit is calculated. And based on the diameter of the probe light beam before beam expansion and the second magnification, the diameter of the probe light beam after beam expansion by the second adjustment unit is calculated, and then the diameter of the probe light beam before the focusing unit is calculated. Based on the diameter of the excitation beam before beam expansion and the diameter of the excitation beam after beam expansion, the far-field divergence angle of the excitation beam after beam expansion is obtained; and based on the diameter of the probe beam before beam expansion and the diameter of the probe beam after beam expansion, the far-field divergence angle of the probe beam after beam expansion is obtained. Wherein, the first beam waist spacing is the distance between the front focal plane of the first adjustment unit and the beam waist of the excitation beam before the first adjustment unit expands the beam, the second beam waist spacing is the distance between the front focal plane of the second adjustment unit and the beam waist of the probe beam before the second adjustment unit expands the beam, the first magnification is the magnification of the first adjustment unit, and the second magnification is the magnification of the second adjustment unit.

12. A method for adjusting a measuring device, characterized in that, The measuring device used in any one of claims 1 to 7 comprises: The light spot size is obtained by the method for obtaining the light spot size as described in any one of claims 8 to 9, or by the method for obtaining the light spot size as described in any one of claims 10 to 11; Set a threshold range, where the threshold range is the range of variation in the spot size; The calculated size of the light spot formed on the sample to be tested is obtained, and the size of the light spot formed on the sample to be tested is determined according to the threshold range. If the size of the light spot formed on the sample to be tested is not within the threshold range, adjust the expansion of the excitation light beam by the first adjustment unit and / or adjust the expansion of the probe light beam by the second adjustment unit, and / or adjust the focal length of the focusing unit until the adjusted light spot size is within the threshold range.

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